Field of the Invention
The present invention relates to a liquid crystal display device having a touch sensing function integrated to a liquid crystal panel thereof, and having high aperture ratio and good visibility. Moreover, the present invention can provide a liquid crystal display device provided with a touch sensing electrode where a low-resistive copper alloy film pattern is used, which is suitable for an electrode used for a touch sensing, with good light shielding properties of transmitted light and where reflective color of the copper alloy film pattern is substantially black. In other words, the present invention relates to an in-cell type liquid crystal display device in which an electrostatic capacitive type touch sensing function is integrated with liquid crystal cells.
Discussion of the Background
In recent years, liquid crystal display devices or organic EL display devices are desired to have a high aperture ratio to achieve brighter displays and low power consumption. In these display devices, in order to improve display contrast by dividing pixels, usually, a black matrix is used in which as a black material, carbon pigment or the like is dispersed into a photosensitive resin.
(Light Shielding Properties of Black Matrix)
The black matrix is arranged surrounding pixels in order to secure display contrast. To obtain high light shielding properties, generally, the black matrix is formed so as to have a large thickness larger than 1 μm inclusive on a transparent substrate such as of glass. The black matrix is formed of a black resin where a colorant such as carbon pigment is dispersed. In particular, in a frame portion that includes four sides defining the display surface where a plurality of pixels are arranged in a matrix, i.e., a black matrix having a frame shape, high light shielding properties of optical density 5 or more, or 6 or more are desired during transmission measurement. Since light from the backlight is likely to leak from the frame portion, the frame portion is desired to have high optical density which is higher than that of the black matrix formed on the display surface.
(Thinning of Black Matrix)
In a display device used for small mobile equipment such as cellular phones, to provide a high definition display such as 200 ppi (pixel per inch) or more, or 300 ppi or more, thinning of the black matrix is desired as well as high light shielding properties. In the case where the black matrix is designed to have a high definition pattern, the width of pixels becomes narrower for example 30 μm or less. Accordingly, deterioration in planarity of color filers has become apparent due to the thickness of the black matrix. A black matrix in a high definition display device having 300 ppi or more is desired to have a thin line width of 4 μm or less.
For example, since the black matrix has high light shielding properties, it is difficult to stably produce a black matrix pattern having a thin line width of 4 μm or less with a photolithography method. For example, to improve the light shielding properties, from a view point of alignment, it is extremely hard to form the black matrix having a thin line width 4 μm or less by a two-step photolithography process, i.e., with two layers. Two steps of processes for forming the black matrix are likely to cause a change in the line width or display unevenness because of alignment displacement.
In general manufacturing processes of a color filter or the like, to form a plurality of screens on a large-sized transparent substrate, usually, an alignment margin, e.g., ±2 μm is necessary. Therefore, it has been difficult to form the black matrix with two-step photolithography process.
(Touch Sensing Function of Display Device)
As a method for performing direct input to a liquid crystal display device or an organic EL display device, the following methods can be employed. These include a method of attaching a touch panel to these display devices, or a method of providing an element corresponding to a touch sensing function, for example, on a portion touching a liquid crystal layer. The latter is referred to as an in-cell method. The in-cell method includes an electrostatic capacitive method or a method using an optical sensor. The electrostatic capacitive type is often used for an in-cell type touch sensing technique, capable of accepting input from pointers such as a finger or a pen in the display device itself. In this electrostatic capacitive type, a plurality of two pairs of electrode groups described in PTL 1 to PTL 5 are required to detect electrostatic capacitance.    PTL 1: Japanese Patent No. 2653014    PTL 2: JP-A-2010-197576    PTL 3: International Publication No. 2012/073792    PTL 4: International Publication No. 2013/089019    PTL 5: International Publication No. 2013/018736